Cysteines and cystines are used in a wide variety of fields, such as pharmaceutical products, cosmetics, and foods. Since cysteine is an amino acid present in high concentrations mainly in human and animal hair, it has been classically produced by hydrolyzing such hair. However, production of cysteine by fermentation is desired, as with many other amino acids, from the viewpoint of higher product safety and less environmental impact.
Various methods for producing cysteine by fermentation using bacteria belonging to the family Enterobacteriaceae have been reported (Patent Literature 1 and 2). For example, Escherichia coli, which is a bacterium belonging to the family Enterobacteriaceae, has two cysteine biosynthesis pathways: a pathway using a sulfate as a sulfur source (sulfate pathway) and a pathway using a thiosulfate as a sulfur source (thiosulfate pathway) (Non-patent Literature 1).
When cysteine is produced using bacteria belonging to the family Enterobacteriaceae, it is known that, in general, cysteine cannot be efficiently produced even if a medium containing only a sulfate as a sulfur source is used, but that cysteine can be more efficiently produced when a medium containing not only a sulfate but also a thiosulfate as sulfur sources is used.
However, thiosulfates used as sulfur sources are very expensive compared with sulfates. Therefore, there is a need for the development of methods for efficiently producing cysteine using an inexpensive sulfate as a sulfur source.